Generally, a thick metal film has a non-transmission property with respect to incident light. Even though apertures are formed through the metal film, if a size of each aperture is much smaller than a wavelength of the incident light, a light amount transmitted through the metal film is remarkably reduced. However, it is well known that, if the apertures are periodically arranged in the metal film and an arranged period of the apertures has a size of the wavelength of the incident light, the light is efficiently transmitted through the metal film, though each aperture has a smaller size than the wave length of the incident light. Furthermore, as a result of recent research, a spectral position and intensity of such transmission resonance phenomenon is clearly expounded by an existing surface plasmon theory. However, it is a fact that understanding of a microscope in such phenomenon is still lack.
While studying the nanoscopic emission property of such arrays, it was founded that light on a non-illuminated side was mostly emitted from a metal surface outside the apertures with polarization-controlled interference pattern. This observation is in contrast to macroscopic expectations and previous theoretical and experimental works that light should be emitted only from the apertures.
In addition, by a nano-optical experiment performed while varying wavelength and polarization of the incident light, and a size of a geometrical structure of the apertures formed in the metal film, mage system, it was founded that the surface plasmon formed on a metal diffraction grating could be propagated at a distance of a few tens micrometer, while preserving coherence.
And it was also found that, if the polarization and wavelength of the incident light is regulated, a pattern of the light emitted from an air-metal interface could be controlled, and particularly, the pattern can be represented by the square of a sine function in an air-metal (1, 0) mode. As getting farther away from the surface, a distribution of the light emitted at this time is more simplified and thus more similar to a shape of the square of the sine function. A period of the square of the sine function is equal to a lattice constant, and a period of the original sine function before squaring is twice as much as the lattice constant. Since this mode has a form of “lattice constant=wavelength/2”, it is called a half wavelength mode. In the half wavelength surface plasmon mode, it is possible to emit the light in a far range of view contrary to the existing surface plasmon that is restricted to the surface. Therefore, the inventors named the half wavelength surface plasmon ‘radiating surface plasmon’. Since a pattern of the radiating surface plasmon is preserved in a far distance, it can be used for novel lithography.
By a near-field study associated with a light radiation type which is occurred on the air-metal interface when light is irradiated on the metal diffraction grating having a periodic aperture array formed on a dielectric substrate, the inventors obtained ideas as follows: first, the metal diffraction grating can be used as a surface plasmon detecting apparatus as well as a surface plasmon generating apparatus having a well-defined propagation direction. Secondly, if the metal diffraction grating is disposed on a metal film having a well-defined interface, it can be used as a surface plasmon optic apparatus which can effectively reflect, separate and control wave of the surface plasmon. Thirdly, if the wavelength and polarization of the light irradiated on the metal diffraction grating is adjusted, the light radiation type generated from the air-metal interface can be also adjusted. Particularly, since the radiating surface plasmon formed in the air-metal (1, 0) mode and having a half period of the lattice constant can maintains its shape up to a size of a few micron, it can be used as a new etching apparatus. Considering that a role of the surface plasmon improving the efficiency of an optic device is noticed, it is expected that there is a possibility of various applications.